Stacked magnetic core having magnetization curve with sharp knee



U. H. KRABBE ETAL STACKED MAGNETIC CORE HAVING MAGNETIZATI CURVE WITH SHARP KNEE Filed March 19, 1956 Jan. 16, 1962 Unite This invention relates in general to magnetic cores and in particular to magnetic cores for saturable reactors and magnetic amplifiers wherein it is desirable and often required that the magnetization curve of the core have a sharp knee.

Grain oriented magnetic material is available having properties which will give a core a sharp kneed magnetization curve provided the core is made so that the magnetic resistance or reluctance of the joints is insignificant.

Well known are the cores which are wound to the desired shape from a continuous strip of magnetically oriented magnetic material. These cores give a sharp kneed magnetization curve but have the disadvantage that either the windings must be sewed or wound through the core or the core must be cut open to receive preformed windings.

Other well known cores are those wherein E-shaped or U-shaped laminations are used. A disadvantage of each of these types of cores is that the orientation is not --proper in portions of each U-shaped or E-shaped lamination.

Still other well known cores are those built up entirely of rectangular shaped lamination strips to thus better utilize the grain oriented material.

Some of these rectangular strip type cores are constructed in such a way that some of the lamination strips butt up against other lamination strips. A disadvantage of this construction is that these butt joints are not good joints for the purpose of obtaining a sharp kneed magnetization curve. A lap joint is preferable to a butt joint for this purpose.

Other rectangular strip type cores have been constructed to have only lap joints. These cores have yoke strips interleaved one for one with leg strips of equal gauge (thickness) and width. In these cores, the legs and yokes each have equally as much air space as iron space; i.e., the legs and yokes are each 50% filled with the magnetic material and the corners are, of course, 100% filled with the magnetic material. A disadvantage of these cores is that the legs, where the windings are placed, contain only 50% of the amount of magnetic material as the legs of a conventional core, and the magnetic material is thus poorly utilized, in that since the cross section of magnetic material is usually a given design parameter, the average winding length of the windings on these cores is larger than is necessary for the windings on cores constructed according to this invention.

Some rectangular strip cores have been made wherein bundles of leg strips are interleaved with bundles of yoke strips. A disadvantage of this type of core is that the flux must thus travel through the several yoke strips in a bundle of yoke strips before entering a bundle of leg stripsand vice versa. This results in ajoint of relatively high reluctance and thus the interchange of flux between yokes and legs is poor. Such cores do not have a sharp kneed magnetization curve.

This invention overcomes the above disadvantages by providing a core. comprised entirely of rectangular strip laminations of magnetically grain oriented material wherein the yoke laminations and leg laminations are overlaptates Patent'O ice pingly'joined at the corners of the core providing lap joints only (no butt joints, and wherein every leg lamination lappingly engages a yoke lamination, and wherein the leg laminations comprise a greater portion of the thickness of the core than do the yoke laminations, and wherein the yoke laminations are wider than the leg laminations.

It is therefore an object of this invention to provide a magnetic core which is comprised entirely of rectangular laminations of magnetically oriented material and which has a sharp kneed magnetization curve.

Another object of this invention is to provide such a core wherein the windings on the legs may be considerably shorter than otherwise would be the case.

Objects and advantages other than those outlined above will appear from the following detailed description when read in connection with the accompanying drawing, in

which:

FIG. 1 is a plan view of a core constructed in accordance with this invention;

FIG. 2 is a side elevation of the core shown in FIG. 1, and FIGS. 1 and 2 together may be considered to illustrate one embodiment of the invention;

FIG. 3 is a side elevation of the core shown in FIG. 1, and FIGS. 1 and 3 together illustrate a second embodiment of the invention;

FIG. 4 is a side elevation of the core shown in FIG. 1, and FIGS. 1 and 4 together may be considered to illustrate a third embodiment of the invention;

FIG. 5 is a side elevation of the core shown in 'FIG. 1, and FIGS. 1 and 5 together may be considered to illustrate a fourth embodiment of the invention;

FIG. 6 is a plan view of a core constructed in accordance with this invention;

FIG. 7 is a side elevation of the core shown in FIG. 6, and FIGS. 6 and 7 together may be considered to illustrate a fifth embodiment of the invention;

FIG. 8 is a plan viewof a core constructed in accordance with this invention;

FIG. 9 is a side elevation of the core shown in FIG. 8, and FIGS. 8 and 9 together may be considered to illustrate a sixth embodiment of the invention;

FIG.. 10 is a plan view of a core constructed in accordance with this invention; and

FIG. 11 is a side elevation of the core shown in FIG. 10, and FIGS. .10 and 11 together may be considered to illustrate a seventh embodiment of the invention.

Referring to FIG. 1 there is shown a core wherein the leg portions comprise rectangular shaped leg laminations 13 magnetically oriented along the long dimension thereof and the yoke portions comprise rectangular shaped yoke laminations 12 magnetically oriented along the long dimension thereof. The yoke laminations 12 are wider than the leg laminations 13.

Referring to FIG. 2, the core is built up by laying or stacking two layers of leg laminations 13, then one layer of yoke laminations 12 to overlap the leg laminations, then two layers of leg laminations 13, then one layer ofyoke laminations 12, etc. This is shown as for the greater number of layers of one preferred core. Still more layers generally would be used repeating the sequence of building and a bottom yoke may be added to the core. There are thus, in this modification, a greater number of leg laminations than yoke laminations. The thickness or gauge of the yoke laminations is equal to the thickness or gauge of the leg laminations.

In FIG. 2, the ratio of number of leg laminations to the number of yoke laminations is 2 to 1. The filling or percentage thickness, of iron to overall cross section of the built up thickness of the core is therefore as follows. The corner. portions of the core are filled with iron. The yoke portions of the core are about 34% filled with iron, and the leg portions of the core are about 66% filled with iron. To obtain equal cross sections of the magnetic material in the yoke portions and in the leg portions the width of the yoke laminations 12 are made greater than the width of the leg laminations 13 by the ratio of the total thickness of all the leg laminations to the total thickness of all the yoke laminations. In the embodiment of FIG. 2, the width of the yoke laminations is thus twice the width of the leg laminations.

FIGS. 1 and 3 together illustrate another embodiment of the invention wherein the filling is about 34% in the yoke portions of the core and about 66% in the leg portions of the core.

In this modification, as is illustrated in FIG. 3, the thickness or gauge of the leg laminations is twice that of the yoke laminations, and there are an equal number of yoke and leg laminations. The core is built up by stacking one layer of leg laminations, then one layer of yoke laminations, etc. The ratio of the total thickness of the leg laminations to the total thickness of the yoke laminations is 2 to 1. The width of the yoke laminations is therefore preferred to be twice the width of the leg laminations to obtain an equal cross section of magnetic material in the yoke portions and leg portions.

FIGS. 1 and 4 together illustrate an embodiment of the invention similar to the embodiment illustrated in FIGS. 1 and 2 in that the yoke laminations and the leg laminations are of equal gauge and there being a greater number of leg laminations than yoke laminations.

The core, as shown in FIG. 4, is built up by stacking or laying one layer of leg laminations, then one layer of yoke laminations, then two layers of leg laminations, then one layer of yoke laminations, etc. This results in a filling of 40% in the yoke portions of the core and 60% in the leg portions of the core. The ratio of total leg lamination thickness to total yoke lamination thickness is 3 to 2. To obtain a core with equal cross sections of magnetic material in the leg and yoke portions, the yoke laminations are made of a width 1% times the Width of the leg laminations.

FIGS. 1 and 5 together illustrate an embodiment of the invention similar to the embodiment shown in FIGS. 1 and 3 in that there are an equal number of leg and yoke laminations, but wherein some of the leg laminations are thicker than the yoke laminations.,

The core, as illustrated in FIG. 5, is built up by laying or stacking one layer or normal gauge leg laminations, then one layer of normal gauge yoke laminations, then one layer of double gauge leg laminations, then one layer of normal gauge yoke laminations, etc. This results in a filling of 40% in the yoke portions of the core and 60% in the leg portions of the core. An equal number of leg and yoke laminations are used, but the gauge or thickness of every other one of the leg laminations is double that of the yoke laminations and that of the other leg laminations. The ratio of the total leg lamination thickness to the total yoke lamination thickness is 3 to 2. To obtain an equal cross section of magnetic ma terial in the leg and yoke portions of the core, the yoke laminations may be made 1 /2 times as wide as the leg laminations.

In all of the embodiments shown, a magnetic core is built up entirely of rectangular leg and yoke laminations of magnetically oriented steel joined at their ends in only overlapping engagement. There are no butt joints, only lap joints. The reluctance of the joints therefore is low and thus favorably contributes to obtaining a sharp kneed magnetization curve as the sharpness of the knee is determined in these cores by the characteristics of the material since the influence of air in the magnetic circuit is reduced.

The yoke laminations each lappingly engage a leg lamination. There is thus individual engagement of the yoke and leg laminations and not just bundle engagement as in some prior art cores where the outside yoke lamination of a bundle of yoke laminations engages the outside leg lamination of a bundle of leg laminations. The individual engagement of every yoke lamination with a leg lamination reduces the reluctance of the joints and makes the interchange of flux between yokes and legs easier, and thus favorably contributes to obtaining a sharp kneed magnetization curve.

The total thickness of the leg laminations is greater than the total thickness of the yoke laminations. This is ac complished by either having more leg laminations than yoke laminations or by having leg laminations of greater thickness than the yoke laminations. A combination of these two methods can be used. The leg portions of the core thus have a greater filling of iron than the yoke pertions of the core as distinguished from an equal filling of iron in yokes and legs as is the case in the prior artcores; Also, as the yoke laminations are Wider than the leg laminations, the leg laminations are thus narrower than they would be in a comparative prior art core. The greater filling or percentage iron combined with a tiar rower width allows the windings placed on the legs to be shorter than would be needed in the prior art cores.

FIGS. 6 and 7 together illustrate another embodiment of the invention. Here, two cores are each constructed as taught in FIGS. 1 and 2 and are placed together to form an aggregate type three legged core. The two center legs 13 together form a single center leg portion which may be embraced by a winding. This type of core commonly used in the construction of magnetic amplifiers wherein each of the outside legs 13 carries a re-- actance winding and the center leg portion comprising both the inner legs 13 carries a control winding.

FIGS. 8 and 9 together illustrate another embodiment, of the invention. The core is built up taught by FIGS. 1 and 4 and a-three legged shell type core is formed. The center leg has a width equal to twice that of the outside legs 13. This type of core is commonly used in magnetic amplifiers wherein the center leg 130 carries a control winding and wherein each of the outside legs 13 carries a reactance winding.

FIGS. 10 and 11 together illustrate another embodi ment of the invention. The core is built up according to the teaching of FIGS. 1 and 3. There are, however, three legs insteadof two. The core is of a three legged three phase type which can be used, for example, in saturable' reactors and magnetic amplifiers.

It will be apparent to those skilled in the art that various changes and modifications may be made in the embodiments of the invention illustrated and described herein without departing from the spirit of the invention or from the scope of the appended claims.

It is claimed and desired to secure by Letters Patent:

1. A magnetic core comprising rectangular leg laminations of magnetically oriented material and rectangular yoke laminations of magnetically oriented material, said leg and yoke laminations being overlappingly engaged at their ends to form only lap joints in the corners of the core, each of said yoke laminations lappingly engaging at least two of said leg laminations, said yoke laminations being wider than said leg laminations, there being at least as many of said yoke laminations as there are of said leg laminations, said leg laminations being thicker than said yoke laminations.

2. A stacked magnetic core having a sharp knee saturation curve comprising a plurality of lamination layers, each of said layers consisting of only rectangular yoke laminations and of only rectangular leg laminations, each of said laminations being of magnetically oriented material and having a preferred direction of magnetization in its respective lengthwise direction, the end portions of said leg laminations engaging said yoke lamination-s only in overlapping superposition, said yoke laminations being wider than said leg laminations, and the total thickness of all of said leg laminations comprising a greater portion of the built up thickness of said core in the manner than is comprised by the total thickness of all of said yoke laminations.

3. A stacked magnetic core having a sharp knee saturation curve comprising a plurality of lamination layers, each of said layers consisting of only rectangular yoke laminations and of only rectangular leg laminations, each of said laminations being of magnetically oriented material and having a preferred direction of magnetization in its respective lengthwise direction, the end portions of said leg laminations engaging said yoke laminations only in overlapping superposition, and the total thickness of all of said leg laminations comprising a greater portion of the built up thickness of said core than is comprised by the total thickness of all of said yoke laminations, said yoke lamina-tions being wider than said leg laminations by the ratio of the total thickness of all the leg laminations to the total thickness of all the yoke laminations.

4. A rectangular magnetic amplifier laminated core comprising a plurality of strips of grain oriented metal, each side of said core being formed of superposed pairs of strips, the ends of each pair being separated from the ends of an adjacent pair by single strips forming the ends of said core.

5. A rectangular magnetic amplifier laminated core comprising a plurality of superposed pairs of elongated strips of longitudinally grain oriented metal disposed to form the sides of said core and a plurality of elongated strips of longitudinally grain oriented metal disposed to form the ends of said core, said second strips being alternately disposed with said first named pairs of strips in Qtld overlapping relation separating each said pair of strips from adjacent pairs of strips.

6. A rectangular magnetic amplifier laminated core of the character described in claim 5, further characterized in that said elongated strips forming the ends of said core have a width substantially twice as great as the width of said strips forming the sides of said core.

7. A magnetic amplifier core comprising three parallel spaced leg members, the center leg of said members being of a width substantially twice that of the two outer members, each of said leg members being formed of a plurality of superposed pairs of elongated strips of longitudinally grain oriented metal and a plurality of elongated strips of longitudinally grain oriented metal disposed to form the ends of said core, said second named strips being alternately disposed with said first named pairs of strips in end overlapping relation to separate each said pair of strips from adjacent pairs of strips.

8. A magnetic amplifier laminated core comprising adjacent rectangular core sections disposed with one leg of each section in juxtaposed relation, each said rectangular core section being formed of a plurality of pairs of elongated strips of longitudinally grain oriented metal disposed to form the sides of said core section and a plurality of elongated strips of longitudinally grain oriented metal disposed to form the end of said core section, said second strips being oppositely disposed with said first named pairs of strips in end-overlapping relation.

9. A magnetic amplifier laminated core comprising adjacent rectangular core sections disposed with one leg of each section in juxtaposed relation, each said rectangular core section being formedof a plurality of pairs of elongated strips of longitudinally grain oriented metal disposed to form the sides of said core section and a plurality of elongated strips of longitudinally grain oriented metal disposed to form the end of said core section, said second strips being oppositely disposed with said first named pairs of strips in end-overlapping relation to separate each said pair of strips from adjacent pairs of strips.

10. A stacked magnetic core having a sharp knee characteristic, said core having, as an elemental core figure, two layers of leg laminations, a single layer comprising yoke laminations exclusively, said layer of yoke laminations separating said two layers of leg laminations, said layers being of substantially equal thickness, the cross section of magnetic material in said single yoke layer being approximately equal to the combined cross section of both of said leg lamination layers.

11. A stacked magnetic core having a sharp knee characteristic, said core having, as an elemental core figure, two layers of leg laminations, each of said layers of leg laminations comprising two laminations spaced apart to form opposite sides of a rectangular figure, a single layer comprising yoke laminations exclusively, said yoke laminations being positioned to form opposite ends of said rectangular figure, said single layer of yoke laminations separating said two layers of leg laminations, said layers being of substantially equal thickness, the cross section of magnetic material in said single yoke layer being approximately equal to the combined cross section of both of said leg lamination layers.

12. A stacked magnetic core having a sharp knee characteristic, said core having as an elemental three layer rectangular core figure, two layers of laminations forming legs on opposite sides of said rectangular figure, a single layer comprising exclusively laminations forming yokes at opposite ends of said figure, said single layer of yoke laminations separating said two layers of leg laminations, said layers being of substantially equal thickness, said yokes being wider than said legs to present substantially the same cross section of magnetic material to a flux path as the combined cross section of both of said leg lamination layers.

References Cited in the file of this patent UNITED STATES PATENTS 567,250 Moody Sept. 8, 1896 2,393,038 Forbes Jan. 15, 1946 2,896,181 Zwelling July 21, 1959 2,929,038 Sonesson Mar. 15, 1960 FOREIGN PATENTS 820,769 Germany Nov. 12, 1951 

